The goal of this research program is to develop a mass spectrometry technique for the determination of bioaerosol concentration in air. The work is divided into three parts. First, an off-line method for microbe and bioaerosol ionization will be developed which uses a liquid matrix for matrix-assisted laser desorption ionization (MALDI). Second, the liquid matrix method will be used with an on-line aerosol mass spectrometer that detects single particles in a known air volume and tallies the number of bioaerosol particles. Third, bioaerosols will be collected and cultured to determine the number of colony forming units (CFU) in a given volume. The results will be compared to those obtained with the aerosol mass spectrometer.